Schizophrenia is a chronic and devastating mental disorder that affects 0.5-0.8 percent general population and over 2 million people in the United States. The current treatment regimen depends on D2 dopamine receptor-targeted drugs that are partially effective on symptoms and cause severe side effects, leading to high treatment discontinuation and relapse. Phosphodiesterase 10A (PDE10A) is emerging as a novel drug target for schizophrenia that promises the development of therapeutics with improved efficacy and less side effects. To develop a pipeline of PDE10A inhibitors, pharmaceutical and biotech companies are depending heavily on cell-free enzymatic assays and structure-based drug design. Although cell-based high-throughput screening (HTS) assays for PDE10A would greatly accelerate the drug discovery process and assist in discovering drug candidates with diverse mechanisms of actions and better pharmacological properties, there are no currently commercial products available to the pharmaceutical industry. Codex Biosolutions has a proprietary cAMP biosensor technology (ACTOne) that has been successfully developed into a cell-based assay for screening PDE4 inhibitors in a 1536-well HTS campaign. In this SBIR phase I funding, our objective is to extend the initial success to establish a PDE10A cell-based assay that will be used by the industry to develop innovative therapeutics for schizophrenia disease. We will conduct all the research in our facilities located in Maryland and New Jersey, which are equipped with all necessary resources to complete the project. We will also have Dr. Hanting Zhang from Departments of Behavioral Medicine & Psychiatry at West Virginia University, an expert on PDE research, to consult us on the project. We propose the following four specific aims for SBIR Phase I. 1. Generate stable HEK293-CNG-TSHR-PDE10A cell line. 2. Knock out PDE4D and PDE4B genes to generate HEK293-CNG-TSHR-PDE10A-PDE4D-/--PDE4B-/- cell line (PDE10A cell line). 3. Adapt the PDE10A cell line to the 384-well HTS format. 4. Perform high-throughput screening of the compound library to evaluate the assay performance in identifying known PDE10A inhibitors. The successful completion of Phase I will pave the way to extend the same technology to other PDE isoforms, leading to the establishment of a repertoire of selective cell-based assays for individual PDE variants that will serve drug discovery projects targeting broad therapeutic areas including CNS, inflammation, metabolism, and cancer.